There are some things that will forever stick with you. You can never forget exactly where you were and what you were doing when you heard the news. For many, the Saturday evening when we heard the verdict in the case of George Zimmerman—the so-called neighborhood watchman who killed 17-year-old Trayvon Martin on February 26, 2012—is one of those times. That gut-wrenching moment was three years ago today, on July 13, 2013.

I was with friends, slightly drunk after a day party, huddled together under a blanket on a comfy sectional. Loud and boisterous most of the day, we quietly watched cable news, speaking up only to pray that our supposed “post-racial” America would redeem itself that day, that it would show us that it was impossible to kill a Black kid for no reason wearing a hoodie that supposedly made him look like “a suspicious person.” But we were quickly reduced to tears and curses when we learned that a six-person jury in Sanford, Florida, had decided that Zimmerman was not guilty of second-degree murder or manslaughter.

Black Americans everywhere reacted with disgust at the system and fear for their own hoodie-clad children. One of those reactions came in the form of a Facebook post. Jelani Cobb, writing for The New Yorker, explains how Alicia Garza and Patrisse Cullors crafted the hashtag #BlackLivesMatter:

Garza has a prodigious social-media presence, and on the day that the Zimmerman verdict was handed down she posted, “The sad part is, there’s a section of America who is cheering and celebrating right now. And that makes me sick to my stomach. We gotta get it together y’all.” Later, she added, “Btw stop saying we are not surprised. That’s a damn shame in itself. I continue to be surprised at how little Black lives matter. And I will continue that. Stop giving up on Black life.” She ended with “Black people. I love you. I love us. Our lives matter.”

Garza’s friend Patrisse Cullors amended the last three words to create a hashtag: #BlackLivesMatter. Garza sometimes writes haiku—she admires the economy of the form—and in those four syllables she recognized a distillation not only of the anger that attended Zimmerman’s acquittal but also of the animating principle at the core of Black social movements dating back more than a century.

It wasn’t long before that moment on social media morphed into a real life movement, birthing the Black Lives Matter network and bringing together thousands of Black people and allies to fight for “the validity of Black life,” as it says on the national organization’s website.

On this day, three years ago, hope was born out of despair. Where were you on that day? Where will you be when equality comes?